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Understanding Neurons: Communication in the Nervous System

This section explores how neurons communicate with each other through synapses, highlighting both electrical and chemical synapses. It delves into the mechanisms of synaptic transmission, including the roles of neurotransmitters and ion channels. Excitatory and inhibitory synapses, the summation of post-synaptic potentials, and the influence of various neurotransmitters like acetylcholine and biogenic amines are discussed. Additionally, it touches on the structure and function of the central and peripheral nervous systems, emphasizing the specialization of the vertebrate brain.

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Understanding Neurons: Communication in the Nervous System

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  1. P. Ch 48 – Nervous Systempt 2

  2. Neurons communicating with other cells • Neurons communicate with other cells at synapses • Electrical synapse- • Direct communication from pre to post synaptic cell • Gap junctions connect cells and ion currents flow between cells

  3. Chemical Synapse • Much more common in vertebrates & most invertebrates • Action potential reaches synaptic terminal • This depolarization causes Ca+ to rush into neuron through voltage gated calcium channels

  4. Chemical Synapse • Synaptic vesicles fuse with presynaptic membrane and release neurotransmitters. • Neurotransmitter diffuses across synaptic cleft and binds to ligand gated ion channels in second neuron. • Ligand gated ion channels open, generating a post-synaptic potential • Neurotransmitter is removed quickly – by enzymes or by surrounding cells uptake

  5. 2 1 3 4 Presynapticcell Postsynaptic cell Axon Synaptic vesiclecontainingneurotransmitter Postsynapticmembrane Synapticcleft Presynapticmembrane K Ca2 Voltage-gatedCa2 channel Ligand-gatedion channels Na

  6. Excitatory synapses • Some synapses are excitatory – they increase the likelihood that the axon of the postsynaptic neuron will generate an action potential • Opens channels that allow Na+ to enter & K+ to leave cell, so • EPSP – excitatory postsynaptic potentiial • Electrical change caused by this binding of neurotransmitter to receptor

  7. Inhibitory synapses • Some synapses are inhibitory – they make it more difficult for the postsynaptic neuron to generate an action potential • Opens channels that allow K+ to rush out of cell and Cl- to enter cell, so • IPSP – inhibitory postsynaptic potentiial • Electrical change caused by this binding of neurotransmitter to receptor

  8. Summation of postsynaptic responses • A single EPSP is usually not enough to produce an action potential • Summation = the additive effect of postsynaptic potentials • The axon hillock is the neuron’s integrating center • Temporal summation • Spatial summation

  9. Indirect synaptic transmission • In some synapses, a neurotransmitter binds to a metabotropic receptor , not directly to an ion channel • Binding of a neurotransmitter to a metabotropic receptor activates a signal transduction pathway in the postsynaptic cell involving a second messenger

  10. Indirect synaptic transmission • Compared to ligand-gated channels, the effects of second-messenger systems have a slower onset but last longer

  11. Neurotransmitters • Many different types – 5 main groups: • Acetylcholine • biogenic amines • amino acids • Neuropeptides • gases • One neurotransmitter can have more than a dozen different receptors

  12. Acetylcholine • Acetylcholine is a common neurotransmitter in vertebrates and invertebrates • It is involved in muscle stimulation, memory formation, and learning • Released at neuromuscular junctions • Can be inhibitory or excitatory

  13. Amino Acids & Gases • Amino acid neurotransmitters are active in the CNS and PNS • Known to function in the CNS are • Glutamate • Gamma-aminobutyric acid (GABA)- thought to be transmitter at most inhibitory synapses in brain • Glycine • Gases such as nitric oxide and carbon monoxide are local regulators in the PNS

  14. Biogenic Amines • Biogenic amines are derived from amino acids • include • Epinephrine • Norepinephrine • Dopamine • Serotonin • They are active in the CNS and PNS

  15. Neuropeptides • Several neuropeptides, relatively short chains of amino acids, also function as neurotransmitters • Neuropeptides include substance Pand endorphins,which both affect our perception of pain • Opiates bind to the same receptors as endorphins and can be used as painkillers

  16. Nervous system • Central Nervous system – • Brain & spinal cord • Peripheral nervous system- nerves that communicate motor & sensory signals thru body

  17. Vertebrate brain specialization Cerebrum – 2 hemispheres, higher brain functions such as thought & action

  18. Vertebrate brain specialization Cerebellum – helps coordinate movement, posture, balance

  19. Vertebrate brain specialization Brainstem – controls homeostatic functions such as breathing rate, heart rate, blood pressure. Conducts sensory & motor signals between spinal cord & higher brain centers

  20. Allan Jones: A map of the brain • http://www.ted.com/talks/allan_jones_a_map_of_the_brain.html

  21. The mysterious workings of the adolescent brain • http://www.ted.com/talks/sarah_jayne_blakemore_the_mysterious_workings_of_the_adolescent_brain.html

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